Endoscopic surgical instruments are often preferred over traditional open surgical devices since a smaller incision tends to reduce the post-operative recovery time and complications. Consequently, significant development has gone into a range of endoscopic surgical instruments that are suitable for precise placement of a distal end effector at a desired surgical site through a cannula of a trocar. These distal end effectors engage the tissue in a number of ways to achieve a diagnostic or therapeutic effect (e.g., endocutter, grasper, cutter, staplers, clip applier, access device, drug/gene therapy delivery device, and energy device using ultrasound, RF, laser, etc.).
Known surgical staplers include an end effector that simultaneously makes a longitudinal incision in tissue and applies lines of staples on opposing sides of the incision. The end effector includes a pair of cooperating jaw members that, if the instrument is intended for endoscopic or laparoscopic applications, are capable of passing through a cannula passageway. One of the jaw members receives a staple cartridge having at least two laterally spaced rows of staples. The other jaw member defines an anvil having staple-forming pockets aligned with the rows of staples in the cartridge. The instrument includes a plurality of reciprocating wedges which, when driven distally, pass through openings in the staple cartridge and engage drivers supporting the staples to effect the firing of the staples toward the anvil.
Generally, a single closing stroke followed by a single firing stroke is a convenient and efficient way to perform severing and stapling. However, in some instances, multiple firing strokes are desirable. For example, surgeons select a length of staple cartridge for the desired length of cut from a range of jaw sizes. Longer staple cartridges require a longer firing stroke. Thus, to effect the firing, a hand-squeezed trigger is required to exert a larger force for these longer staple cartridges in order to sever more tissue and drive more staples as compared to a shorter staple cartridge. It would be desirable for the amount of force to be lower and comparable to shorter cartridges so as not to exceed the hand strength of some surgeons. In addition, some surgeons, not familiar with the larger staple cartridges, may become concerned that binding or other malfunction has occurred when an unexpectedly higher force is required.
In U.S. patent application Ser. No. 11/066,371 entitled “SURGICAL STAPLING INSTRUMENT HAVING AN ELECTROACTIVE POLYMER ACTUATED SINGLE LOCKOUT MECHANISM FOR PREVENTION OF FIRING” to Shelton filed 25 Feb. 2005, the disclosure of which is hereby incorporated by reference in its entirety, an EAP lockout actuator is advantageously incorporated into an implement portion to block a firing member to prevent firing. Thereby, an undesirable situation is avoided such as when full or partial firing occurs, causing severing of clamped tissue, without the surgical instrument being capable of forming staples.
While such an EAP lockout mechanism incorporated into the implement portion has certain advantages, it is desirable in some instances to provide an alternative or an additional lockout mechanism.
Consequently, a significant need exists for an improved surgical stapling and severing instrument that prevents inadvertent firing (i.e., severing and stapling) when a either the instrument or the surgeon are not prepared to fully sever and staple clamped tissue.